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  • The value of infrared thermography for research on mammals:previous applications and future directions

    DOMINIC J. MCCAFFERTYDepartment of Adult and Continuing Education, Faculty of Education, University ofGlasgow, 11 Eldon Street, Glasgow G3 6NH, UK

    ABSTRACT1. Infrared thermography (IRT) involves the precise measurement of infrared radiationwhich allows surface temperature to be determined according to simple physical laws. Thisreview describes previous applications of IRT in studies of thermal physiology, veterinarydiagnosis of disease or injury and population surveys on domestic and wild mammals.2. IRT is a useful technique because it is non-invasive and measurements can be made atdistances of 1000 m to count large mammals.Detailed measurements of surface temperature variation can be made where large numbers oftemperature sensors would otherwise be required and where conventional solid sensors cangive false readings on mammal coats. Studies need to take into account sources of error dueto variation in emissivity, evaporative cooling and radiative heating of the coat.3. Recent advances in thermal imaging technology have produced lightweight, portablesystems that store digital images with high temperature and spatial resolution. For thesereasons, there are many further opportunities for IRT in studies of captive and wild mammals.

    Keywords: disease, infrared thermography, injury, population surveys, temperaturemeasurement, thermal physiology

    Mammal Review (2007), 37, 207223doi: 10.1111/j.1365-2907.2007.00111.x

    INTRODUCTIONInfrared thermography (IRT) involves the precise measurement of infrared radiation emittedby an object, which allows the surface temperature to be determined according to relativelysimple physical laws and known properties of the surface (see Speakman & Ward, 1998).Specialized thermographic cameras produce images that show the variation in temperature ofa surface by representing different temperatures with a grey or coloured shaded scale (Fig. 1).Although thermal imaging was developed principally for industrial, medical and militaryapplications (Burnay, Williams & Jones, 1988), it has been used to study many animal groupsincluding insects, reptiles, birds and mammals (see McCafferty et al., 1998).

    Infrared thermography can examine many different aspects of thermal physiology, diag-nose injury and disease and is a useful technique for counting animal populations. The greatadvantage of IRT in animal research is that measurements can be made without touching ordisturbing the animal and depending on the instrument type and application, measurementscan be made either at close range (1000 m). Detailed measure-ments of the temperature variation of mammals can be made where large numbers oftemperature sensors would otherwise be required. Conventional solid probes can also give

    Correspondence: D. J. McCafferty. E-mail: d.mccafferty@educ.gla.ac.uk

    Mammal Rev. 2007, Volume 37, No. 3, 207223. Printed in Singapore.

    2007 The Author. Journal compilation 2007 Mammal Society, Mammal Review, 37, 207223

    mailto:mccafferty@educ.gla.ac.uk

  • false readings due to the difference in heat capacity between sensor and coat or throughdisruption of the hair fibres by sensors (Cena, 1974; Mohler & Heath, 1988). Previously, Cena& Clark (1973) outlined important theoretical aspects of this technique for research ondomestic and zoo animals, Yang & Yang (1992) reviewed biomedical and veterinary appli-cations and Speakman & Ward (1998) gave an account of the principles of IRT and dem-onstrated its usefulness for studying thermoregulation. More recently, Kastberger & Stachl(2003) highlighted several interesting veterinary and physiological applications.

    L1

    20.0

    60.0 C

    30

    40

    50

    FLIR Systems

    C

    202224262830323436384042444648505254565860

    Label Min Max Avg

    L1 20.0 57.9 40.3

    (a)

    (b)

    (c)

    Fig. 1. Photograph (a) of Grantszebra Equus burchelli boehmi withcorresponding infrared image (b) infull sun. The temperature profile L1displayed in the graph below (c)shows the variation in temperatureacross the body, with black stripesmore than 10 C warmer than whitestriped areas of the coat. Mean airtemperature = 28.3 C, relativehumidity = 44%, solarradiation = 860 Wm-2 and windspeed = 0.3 ms-1.

    208 D. J. McCafferty

    2007 The Author. Journal compilation 2007 Mammal Society, Mammal Review, 37, 207223

  • The aim of this review was to examine the value of thermal imaging for research onnon-human mammals. In particular, this paper brings together findings from physiological,ecological and veterinary investigations to generate new ideas on how to use IRT to inves-tigate wild mammal populations. This review is timely given recent advances in thermalimaging technology and a reduction in the cost of these devices, both of which will providefuture research opportunities.

    APPLICATIONSFor this review, a literature search was undertaken using ISI Web of KnowledgeSM (http://wok.mimas.ac.uk/). This was followed by compiling a reference list from each of these papersto include older studies that may not have been listed in current electronic databases andsupplementing these with other known studies. This is therefore not an exhaustive list as thisis a widely used technique, but it is likely to cover a large proportion of the main empiricalstudies to date. For the purposes of this review, studies on humans and closely related clinicalapplications were not considered.

    Seventy-one empirical studies using IRT on mammals since 1968 (Tables 13) were exam-ined. These studies involved domestic and wild mammals from 11 mammalian orders. Two-thirds of the studies involved terrestrial species and a third were on aquatic mammals, mostlymarine species. These included 34 studies on thermal physiology (48%), 19 involving veteri-nary diagnosis of disease and injury (27%) and 18 population surveys (25%). Seventy per centof studies were on captive mammals.

    Thermal physiologyInfrared thermography has been used to examine many different aspects of thermoregulation(Table 1) and much of this work has focused on identifying parts of the body with relativelyhigh temperature which can be related to an animals anatomy and physiology. This hassignaled that the head is a major source of heat loss for most species of mammals and alsoidentified the importance of appendages in controlling heat loss. These studies demonstratethe clear link between surface temperature and underlying blood circulation and brownadipose tissue, as well as the role of fur in reducing heat loss from the skin surface. Manystudies have examined the relationship between body surface temperature and air tempera-ture. However, a novel approach with IRT has been to examine the relationship betweenenvironmental temperature and the sensitivity of vibrissal follicles in seals and dolphins(Dehnhardt, Mauck & Hyvrinen, 1998; Mauck, Eysel & Dehnhardt, 2000). These studiesdemonstrated that even in the cold, blood is circulated to these areas to maintain the functionof these essential sensory organs.

    A major strength of IRT is its ability to relate changes in surface temperature to particularphysiological states or associated with certain behaviours such as huddling or vocalization.Recent studies have also shown that IRT is capable of detecting surface temperature changesin response not only to physical activity but also to fear. Particularly significant were thefindings of Nakayama et al. (2005) which showed that changes in facial surface temperaturepatterns of Rhesus monkeys Macaca mulatta occurred in response to the threat of capture.IRT is particularly suited to examining changes in surface temperature during activities suchas running, flying and even swimming. The latter application on marine mammals was aninteresting applied study to examine the significance of changes in circulation associated withexercise in dolphins when chased and captured in the Pacific tuna fishery (Pabst et al., 2002).This study found that dolphins increased their rate of heat dissipation from dorsal fins to theenvironment from the start of the chase. During prolonged chases, animals had higher skinsurface temperatures, presumably as a result of greater blood flow to these areas.

    The value of infrared thermography for research on mammals 209

    2007 The Author. Journal compilation 2007 Mammal Society, Mammal Review, 37, 207223

    http://wok.mimas.ac.ukhttp://wok.mimas.ac.uk

  • Tab

    le1.

    The

    rmo-

    phys

    iolo

    gyst

    udie

    sus

    ing

    IRT

    onca

    ptiv

    e(c

    )an

    dw

    ild(w

    )m

    amm

    als

    show

    ing

    mea

    sure

    men

    tsta

    ken,

    dist

    ance

    (m)

    and

    imag

    ing

    syst

    emus

    ed

    Spec

    ies

    Mea

    sure

    men

    tD

    ista

    nce

    Cam

    era

    type

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    hor

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    ndic

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    Exe

    rcis

    ean

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    atlo

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    (196

    8)E

    leph

    ant

    and

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    aL

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    a,E

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    ic

    Col

    oura

    tion

    515

    Aga

    visi

    on68

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    ena

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    (197

    3)P

    olar

    bear

    U.m

    arit

    imus

    cSi

    tes

    ofhe

    atlo

    ss

    AG

    AT

    herm

    ovis

    ion

    720

    rt

    isla

    ndet

    al.(

    1974

    )Ja

    ckra

    bbit

    L.c

    alif

    orni

    cus

    cE

    xerc

    ise

    and

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    loss

    A

    GA

    The

    rmov

    isio

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    0-12

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    illet

    al.(

    1976

    )H

    arp

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    wV

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    1979

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    le2.

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    1996

    )C

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    (199

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    anis

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    ange

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    .(20

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    phy.

    The value of infrared thermography for research on mammals 211

    2007 The Author. Journal compilation 2007 Mammal Society, Mammal Review, 37, 207223

  • Tab

    le3.

    Mam

    mal

    surv

    eys

    usin

    gIR

    Ton

    capt

    ive

    (c)

    and

    wild

    (w)

    mam

    mal

    ssh

    owin

    gm

    easu

    rem

    ents

    take

    n,di

    stan

    ce(m

    )an

    dim

    agin

    gsy

    stem

    used

    Spec

    ies

    Mea

    sure

    men

    tD

    ista

    nce

    Cam

    era

    type

    Aut

    hor

    Whi

    te-t

    aile

    dde

    erO

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    gini

    anus

    wP

    opul

    atio

    nco

    unts

    300

    Cla

    ssifi

    edC

    roon

    etal

    .(19

    68)

    Whi

    te-t

    aile

    dde

    erO

    .vir

    gini

    anus

    wP

    opul

    atio

    nco

    unts

    300

    Cla

    ssifi

    edM

    cCul

    loug

    het

    al.(

    1969

    )P

    olar

    bear

    U.m

    arit

    imus

    wD

    etec

    tion

    &co

    unts

    150

    Tes

    tB

    rook

    s(1

    972)

    Whi

    te-t

    aile

    dde

    erO

    .vir

    gini

    anus

    wP

    opul

    atio

    nce

    nsus

    300

    Tes

    teq

    uipm

    ent

    Gra

    ves

    etal

    .(19

    72)

    Rin

    ged

    seal

    P.h

    ispi

    daw

    Snow

    lair

    s18

    0F

    LIR

    1000

    AK

    ings

    ley

    etal

    .(19

    90)

    Wal

    rus

    O.r

    osm

    arus

    dive

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    sw

    Num

    bers

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    size

    400

    2400

    DF

    OR

    SB

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    ret

    al.(

    1991

    )W

    hale

    s5

    spec

    ies

    wC

    ount

    san

    dte

    mpe

    ratu

    re10

    70

    AG

    EM

    AT

    herm

    ovis

    ion

    880

    Cuy

    ler

    etal

    .(19

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